Flush or countersunk riveting



Feb. 21, 1939. E. BECKER FLUSH OR GOUNTERSUNK RIVETING Filed.Nov. 7, 1936 Emf/ Beg/raul* [nre/nier'.

Patented Feb. 21, 1939 UNITED STATES PATENT OFFICE Application November 7, 1936,A Serial No. 109,681 In Germany September 18, 1935 1 Claim.

This inventiony relates to flush or countersunk riveting.

The usual flush riveting meets with insuperable difficulties if the sheets to be riveted are so thin 5 that scarcely the conical counter-sunk hole, and at al1 no cylindrical rivet shank, find a place. Even with thicker plates, the strength' of flush riveting is not satisfactory for al1 requirements.

The new riveting process consists in deforming the sheets around the riveting hole, by means of the head of the introduced rivet, into uni-directional conical depressions, and in forming the closing head on the rivet shank on the opposite side of the head. In this connection a rivet having a head which is not of counter-sunk form can be used with special advantage, this head being reshaped into the counter-sunk head during the riveting operation.

The principle underlying the invention is fundamentally applicable for all kinds of rivet connections without regard to the actual wall thicknesses of the parts to be connected. Wall thicknesses down to about 115mm., which are now used in light construction Work, for example in the manufacture of aircraft, are meant by reference in the present specication to thin sheets.

Since this riveting principle, however, is best adapted for tight riveting, it may be used in the construction of floating bodies which, according to their dimensions may have really considerable wall thicknesses. The use of this riveting process then produces a single seam, relatively coarse riveting or rivet pitch. This riveting is best adapted also for other purposes, for example for v the construction of high pressure containers.

The new method of riveting introduces a number of valuable improvements into this technical domain, where it is of greatest importance that it at all provides the possibility of carrying out satisfactory ilush riveting with thin sheets. It complies with the fundamental conditions for obtaining great strengths because large surfaces of material (sheet metal) are gripped; in the case of thin walls and highly loaded riveting the whole surface pressures in the aperture in the sheet are so large that the frictonal resistance is a substantial factor for strength. When the riveted seam is placed under strain the wall parts pressed 5 into conical shape prove to be so stili, that they provide a strong resistance to deformation such as precedes the fracture of the riveted part on overloading. Whereas in usual processes a small Aloss in strength must be allowed for gaining 55 smoothness, the new riveting achieves quite a substantial increase in strength in consequence of the conical stiffening of the sheet remaining under high pressure around the riveting aperture.

The surface smoothness is of the highest qual- 5 ity. This is shown in (1) The evenness of the parts of the sheet in the riveted seam. Any stretching of the material around the rivet, occurring with powerful riveting, is compensated for by the bulging for receivl0 ing the counter-sunk head, which takes up any folding and places the sheets around the riveting aperture under tension.

(2) The uninterrupted transition from rivet head to the surface of the sheet (important for 15 lowering costs of the surface treatment) and, as a consequence thereof, the elimination of the expensive smoothing and grinding operations.

(3) The elimination of open seams between two rivets which effect not only the surface smooth- 20 ness between two rivets. but also prevent tight riveting. I

The stiffening of the edge of the riveting aperture and the tension acting on it permits a wide riveting pitch. 25

No special preparation is necessary for carrying out the new method of riveting. The sheets are bored as usual and fitted with normal rivets. The new features in the riveting operation, including the cone formation at the rivet apertures, 30 are eifected by the tool, which is handled in the usual way for tools operated by striking or by pressure, so that with the use of the new riveting method no change in operation or new installation is necessary, with the exception of obtaining 35 the tools.

The deforming operation during the riveting acts additionally to improve the quality, since at the rivet head the greatest deformation lies at the edge ofthe rivet head and has a gap-closing 40 action, and, with the sheets, the edges of the rivet aperture are most deformed, which produces a high sheet surface pressure.

A further important factor in the use of the new riveting process is to be found in the possibility of adopting measures for'ensuring the durability of thin walled constructional parts, since the thin sheets to be `connected are used for riveting in a protected condition .(by corrosionprotective coatings) the preserving coating not being injured during the connection.

The tool for the now riveting process may consist fundamentally of anvil and snap-head die with hammer, or even of a riveting press with 55 riveting swages. For particularly neat and strong' riveting a counter-sinking die serving as snaphead die or rivet abutment has a cavity which determines the conical shape of th'e pressed part of the sheet and surrounds a head closing die longitudinally movable in it in such a way that the latter enters into the cavity towards the end of the riveting operation, that is generally with great riveting pressure.

A further advantageous detail occurs if the head closing die is mounted so as to project elastically from the swage body and is provided with a centering depression. The tool with the part thus projecting can then be mounted snugly on the rivet shank and centered accurately on it. The centering depression can be formed in an inner ram enclosed 'by the head closing die and pressed forward elastically, which in the striking position at the bottom of the outer sleeve amplifies the depression forming the closing head to a smooth complete shape of the closing head. In this way the shape of the closing head is independent of that of the centering depression, that is it can be adapted particularly well to requirements.

The anvil (or hammer) co-operating with the counter-sinking die may have fundamentally a level surface. For riveting with a riveting machine, together with the formation of the smooth surface at top, a centering in the ilat swage can be provided on the other side supplementary to, or i'n replacement of, the centering present in the counter-sinking die, and may suitably be in the form of an elastically depressable centeringrlng surrounding the ilxed rivet head. The w'orki piece must then be brought under the machine so that in each case the head of an inserted rivet ts into the centering ring, and the countersinking die disposed below and centered thereby roduces then, on mutual approaching of both parts, the correct riveting.

The same construction of tool can be used for all kinds of riveting. It can be so constructed that it is applicable simultaneously for hand riveting, compressed air riveting and machine riveting.

The tool can also operate in any desired position.

(1) On a work table, for example in a perpendicular position (striking head at top) (2) The same in a riveting machine with, however, the working surfaces at top,

(3) In a compressed air hammer, in any desired position on the freely disposed workpiece, or freely suspended workpiece.

A special advantage resides in the use of this tool for the construction of hollow bodies, where the very simply held abutment mass is connected withl the riveting tool for always assuming a common position.

This produces a very simple riveting method comprising the following features:-

(a) Introduction of the rivets from outside,

(b) Smooth surface striking from outside,

(c)r Deformation inside the workpiece.

Further, the possibility of using all kinds of rivets from the semicircular head, which requires the greatest work of deformation, through the flattened round head, to the counter-sunk head, is important.

The accompanying drawing illustrates a number of constructional examples of the invention, taken on central sections wherein:

Figs. l and 2 illustrate on a greatly enlarged scale a simple riveting ram, showing the rivet before and after the blow.

Fig. 3 illustrates a tool having any elastical counter-sinking die.

Fig. 4 illustrates a tool having a counter-sinking die supported by springs.

Fig. 5 illustrates a riveting machine tool with counter-sinking die disposed below and centering ring disposed at top.

According to Figs. 1 and 2 a rivet is placed in the rivet apertures of the sheets to be connected, with the head resting on the level surface of a stationary die 2, and a riveting die I moves with the necessary striking or pressure energy in the direction of the arrow on to the workpiece.

The re-shaping of the parts to be connected is eifected as shown in Fig. 2.

The essential feature in carrying out this riveting operation is the shape of the working surface of the snap-head die I. It comprises a flat face 3, a conical boring 4 and a cavity 5, which is shaped according to the desired shape of the closing head and the dimensions of the swelling or collar 8 of the closing head around the apex of the cone 'I of the sheet; the working surfaces 3 and I determine the re-shaping of the round head into the counter-sunk head of the rivet, and the surface 5 determines the shape of the closing head. If the conical surface l is omitted and the arrangement of the boring is as indicated in dotted lines at l, the cones at the rivet head and on the sheets are also formed in a quite noticeable manner; nevertheless the conical surface I' increases the pressure of the two sheets during the formation of the cone.

In order to obtain at an uninterrupted transition of the counter-sunk hole into the flat, the construction of the edge Il of the die is important. The shape of the working surface of the snap-head die corresponds to the desired reshaping of that part of the rivet which projects during the riveting operation and of the sheets to be connected.

This is the simplest arrangement for carrying out the new method of riveting; it is applicable with equally satisfactory results to hand riveting on the work table with ilxed abutment, as well as -to the freely arranged work-piece with corresponding abutment mass; further, for compressed air tools and rivet presses, and therefore for machine riveting. It can be satisfactorily used for mass production for most riv't connection.

If high requirements as to quality and strength oi' the rivet seam are made, then refined tools. such as are shown in Figs. 3 and 4, can be used.

'I'hese tools are provided with centering devices which come into action on the starting of the riveting operation and ensure coincidence of the axes of the snap-headdie and of the rivets; they have, further, elastic counter-sinking dies which ensure that, during the shaping, rstly, the counter-sinking is effected, and then the formation of the closing head with a simultaneous rigid assembling of the two sheets.

According to Fig. 3 an outer sleeve Il has a thick head 2 which is constructed to receive hammer strokes or for mounting in compressed air tools or riveting presses. and in the boring of which a counter-sinking die I3 is mounted so as to be longitudinally movable and is prevented from falling out by a closure cap Il. The countersinking die I3 contains on its front face a cavity I which takes up material during the shaping. 'I'his cavity can also have the conical shape 4 according to Fig. 2. 'Ihe counter-sinking die I3 is constructed as a stiff spring by'means of a helical slot I6 which has to oier resistance to the deforming pressure, but is resilient in the longitudinal direction on a further increase in pressure for the formation of the closing head. The closing head die I'I is built into the countersinking die so as to be longitudinally displaceable therein. It has at top a widening or thickening I8 which prevents it from falling out and which encloses a weak spring I9 in order to press the die constantly downwards. At bottom the die has a centering boring 20 which on the start of the riveting operation embraces the shank of the rivet. During the riveting operation the tool is placed with the centering depression onto the shank of the rivet and is moved by impact or pressure onto the workpiece resting on the abutment. Thereupon the closing head die rst moves backwards, until the die has completed the shaping of the rivet head and of the sheets; in the further downward movement the head of the closing head die I1 bears against the bottom of the housing I2 and stamps out the closing head. This additional downward movement of the whole tool is taken up by the yielding counter-sinking die.

According to Fig. 4 the toolis fundamentally the same as in the preceding case, only the shaping die I3a is made hollow and is pressed forward by a rear guide member I3b acting through a series of ball segmental springs I3c disposed one behind the other.

Mass riveting is preferably carried out on a riveting machine; in this case it is advantageous to introduce the rivets from above and to transfer the rivet centering to the tool likewise upwardly. For these requirements a tool according to Fig. 5 is suitable. 'I'he shaping tool according to Figs. 1 to 4 is arranged below the workpiece and the abutment is built into the machine die. In order to effect the centering easily from above a centering ring 23 held by a cover 22 is built into the abutment 2| and is pressed downwardly by the spring 24. The boring of the centering ring corresponds to the diameter of the rivet hea'd which, before the riveting, is held in this boring.

During the downward movement of the die the centering ring 23 moves backwards so far that the front of the part 2|, namely its centre pin, comes into line with the part 22 and for many cases also with part 23. The riveting procedure corresponds to that above described with the difference that the shaping tool is here disposed at the bottom and the abutment at top; the same tools from the simplest to the most refined construction can be used.

I claim:

The herein described process for flush riveting thin metal sheets, comprising the steps of forming aligned rivet holes in superimposed sheets, inserting through said holes a solid rivet having a round head with flat inner surface, subjecting the sheet metal overlying the fiat inner surface of the rivet head to a substantial pressure to counter-sink the superimposed sheets about the rivet holes and simultaneously to deform said head into a solid cone seated in and conforming to the counter-sunk recess in the sheets and having its base flush with the corresponding surface of the latter, and upsetting the rivet shank into a closing head.

EMIL BECKER. 

